How many grams of #NaOH# are contained in 200 mL of a 0.400 M solution?

1 Answer
May 26, 2018

Answer:

Approx. #3*g#

Explanation:

By definition....#"concentration"="moles of solute"/"volume of solution"#...and thus concentration has units of #mol*L^-1#..

And following this definition dimensionally, #"moles of solute"="concentration"xx"volume"#..

And so here, this product gives...

#200*mLxx10^-3*mL*L^-1xx0.400*mol*L^-1=underbrace(0.0800*mol)_"moles of solute"#..

And the associated mass is #0.0800*molxxunderbrace(40.00*g*mol^-1)_"molar mass of NaOH"=??*g#

This is why chemists and physicists use units in their numerical calculations; not to confuse students, but to alert them when they have ballsed up a question. If the units didn't simplify to #mol# and #g#, we would know we had made an error...